XXXI] COMPARISON 281 



Osmundaceae or Schizaeaceae: but it is not very materially smaller than 

 that of Dicksonia (64). Finally, the cordate prothallus, and the dehiscence 

 of the antheridia would accord with various relatively primitive Ferns, and 

 does not appear distinctive. The sum of all of these considerations leads to 

 the conclusion that Plagiogyria is a relatively primitive type, but not very 

 closely allied downwards to any one of the known primitive Ferns. The 

 relation to the Schizaeaceae suggested by the axillary involutions in the 

 dictyostelic stem, and in some degree by the structure of the sporangia, is 

 vitiated by their superficial position in Plagiogyria: that to the Osmundaceae 

 is indicated by the basal swellings of the leaves, the stelar structure and 

 dichotomy of the upright stock, the dermal hairs, and particularly by the 

 superficial sorus, as in Todea: but it is negatived by the difference in 

 sporangial structure, and the small spore-output. The relation to other 

 Superficiales such as the C)'atheae does not appear cogent. On reconsidering 

 the question as a whole it seems necessary to constitute Plagiogyria as the 

 only living genus of an independent Family of Plagiogyriaceae, its position 

 being somewhat isolated, but with relations downwards to such Families of 

 the Simplices as the Osmundaceae and Schizaeaceae. 



The relations upwards have already been recognised by various writers. 

 They are \vith such genera as Llavea and Cryptogranime: while these lead 

 on to a large number of Superficiales of the type of Gymnogramme, which 

 constitute a phylum to be discussed later under the collective name of the 

 Gymnogrammoid Ferns. It will, however, be seen as the study of their sori is 

 developed, that there is no near phyletic relation either to the Pteroideae or 

 to the Blechnoideae, notwithstanding the superficial similarity which the 

 fertile pinnae appear to possess in all these three sequences. 



Incidentally the existence of a "mixed" character of the sorus, indicated 

 rather than fully developed, suggests that this state may have been derived 

 directly from a "simple" sorus, without the intervention of a gradate condition. 

 It will be seen later that evidence of a like direct progression is afforded 

 within the genus Dipteris. 



Family. PLAGIOGYRIACEAE Bower, 1924. 



I. Genus. Plagiogyria Y^^^\^ZQ, \'^\<^ ... ... ii species. 



BIBLIOGRAPHY FOR CHAPTER XXXI 



544. KuNZE. Bot. Zeit. 1849, p. 865. 



545. Mettenius. Ueber einige Farngattungen. \\. Phxgiogyria. \Z--)%. 



546. Hooker. Species Filicum. iii, p. 2. 



547. Diels. Naiiirl. Pflanzenfam. i, 4, p. 281. 



548. Bower. Suidies in Phylogeny. I. Ann. of Bot. xxiv, p. 423. 1910. 



549. Lang. Mem. Manch. Lit. and Phil. Vol. 68, Part I, p. 53. 1924. 



